1. Field of the Invention
This invention relates to a fluid pressure control apparatus which is used in a brake system for vehicle, and more particularly to a fluid pressure control apparatus which is used in a brake system provided with an anti-skid control apparatus.
2. Description of the Prior Art
In a brake circuit for vehicle, different control apparatus are arranged for securing the safety on the braking.
One representative example of the control apparatus is a fluid pressure control valve. Another example thereof is an anti-skid control apparatus.
The anti-skid control apparatus controls automatically the brake fluid pressure to prevent the wheel from looking. In the control operation, brake fluid is discharged into a relieving circuit, and it is pressurized and returned to the master cylinder side by a fluid pressure pump.
When the pressurized brake fluid is returned to the master cylinder, the Pulsation of the fluid pressure pump is transmitted through the brake pedal to the driver. The driver feels uncomfortable. Accordingly, it is preferable to arrange a throttle for damping the pulsation of the pressurized brake fluid discharged from the fluid pressure pump.
This Assignee previously proposed the fluid pressure control apparatus for the above described purpose in the Japanese Patent Application No. 69023/1990 which includes, a main body in which an input opening is formed in communication with a master cylinder side and an output opening is formed in communication with a wheel cylinder side a stepped bore made in the main body, in communication with the input opening and output opening a piston slidably fitted into the stepped bore a path for connecting the input opening side of the piston with the output opening side of the piston valve means arranged in the path for limiting the pressure rise of the output opening side, being closed and opened in response to movements of the piston ; a preloaded spring for urging the piston in a direction to open the valve means, a movable body arranged at the output opening side of the piston, being movable in accordance with the movement of the piston, a valve seat onto which the movable body seats with the movement of the piston to the input opening side, and a throttle for throttling the fluid flow towards the input opening side from the output opening side on the seat of the movable valve body, and in which a control piston is provided for moving the movable body to the valve seat towards the input opening side against the spring force of the preloaded spring, receiving the fluid pressure of the output opening side or input opening side of the throttle at its one end, while the valve means is still opened.
In the proposed fluid pressure control apparatus, the control piston receives the output side pressure of the throttle or the input side pressure thereof, and it makes the piston move against the preloaded spring to the position at which the movable body seats on the valve seat, maintaining the fluid pressure control valve opened.
When the control piston is moved to the master cylinder side against the urging force of the preloaded spring with the input side pressure of the throttle or the output side pressure thereof, the throttle is changed over from the inoperative condition into the operative condition.
Accordingly, when the fluid pressure is altered for the change-over of the inoperative condition into the operative condition, the effective fluid pressure receiving areas of the control piston should be changed. Thus, the diameter of the control piston and that of the stepped bore should be changed. The size of the whole apparatus should be large-sized. The respective parts cannot be used in common.